Rotor



Aug. 18, 1931- c. B. coATEs 1,819,228

ROTOR Filed March 26. 1929 'J/// //v a/WW,

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Patented Aug. 18, 1931 UNITED STATES.

PATENT; OFFICE.

CHARLES E. COATES, OF CLEVELAND, OHIO, ASSIGNOR '10 CHICAGO PNEUMATIC13001: 00:01am, 01 NEW YORK, N. 'Y., A CORPORATION OF NEW JERSEY BoronApplication filed. larch 26, 1929. Serial No. 349,958.

This invention relates to squirrel cage rotors of the bar type for usein induction .motors, and more es ecially to rotors of the so-calledcast or in estructible type. Such j rotors, in accordance with thepreferred practice,'have the windings and end rings cast inone pieceupon the core.

Rotors of the described type, as heretofore used, have had absolutelysmooth exteriors It has been discovered that there is a loss ofefiiciency due to undue heating which results from the difiiculty inforcing air through the narrow gap between the rotor and the stator,especially in the When such rotors are used in high frequency motors,especially in the small motors used on portable tools where the gap isabout .015

of an inch, the customar fan on the motor shaft cannot force air trouigh the narrow air gap fast enough or. in su cient quantity to carryaway the heat generated at the high speed of rotation.

' One object of the invention is to improve the cooling of rotors of thedescribed type.

Another object is to produce an improved cooling efl'ect withoutimpairing the operation ofthe motor or weakening the rotor structure.Qther objects will be a parent fromthe detailed description whichollows. I The invention comprises forming the rotor with built-incooling features. These features consist in interrupting the smoothexterior surface of the rotor in a manner to cause movement of airaxially from one end 'of the rotor to the other. In the referredarrangement, spiral grooves, exten ing from one end of the'rotor to theother, are cut in the core portion of the rotor. These grooves may bearranged to extend over and along the bars or cast windings of therotor.

In order to illustrate the invention, one embodiment thereof is shown inthe accompanying drawings, in which:

' Fig. 1 is a perspective view of the improved rotor;

Fig. 2 is a transverse sectional view substantially on the line 2-2 ofFig. 1; and 50 Fig. 3 is an end elevational view.

terior of the core coul 'In the embodiment of the invention shown in thedrawings, the rotor comprises a laminated core 4, each plate of which isperforated or otherwise cut away as indicated at 5, to receive the barsor cast windings 6 which extend the full length of the core andterminate in integral end rings 7 which, in the present instance, aretapered outwardly from their bases which engage the end plates of thelaminated core 4 and cover the bar openings 5. As clearly indicated inFigs. 1 and 3, the end rings are of less diameter than the plates of thecore so that the latter projects somewhat therebeyond. Slots 8,extending from one end ring to the other, are provided in the portion ofthe rotor which extends beyond the end rings, these slots being cutsubstantially to the level of the end rings and on a slight curve orspiral. Slots 8 are regularly placed and dis- [0 posed in parallelism sothat when the rotor 7 turns it has the effect of an. air screw inforcing air from one end of the rotor to the other.

The slots may be-variously made but it is 15 simplest to mill the slotsthrough after the windings and end rings are secured in place,preferably by casting the same upon. the rotor core in one operation. Bypreference the slots are cut over the bars or cast windings as shown. Inmounting the fan upon the rotor, attention must be given to thedirection of rotation of the rotor so that the inclination of the spiralgrooves 8 will be 4 such as to assist the fan in moving the air asthrough the airgap and not to oppose the action of the fan.

I am aware that in the conventional form of wire wound rotor the slotsfor the wind ings are cut throughthe eriphery of the rotor and that,when wedges are inserted to hold the windings in place, a groove is leftin the rotor somewhat similar to the cooling means herein disclosed. Butsuch an arrangement is the result of necessity, for only by leavingopenin '5 through the exthe windings be wound and inserted. Thus theslots in the core have always been looked upon as neces sary evils andmuch trouble has resulted 10D from the difliculties involved in securelywedging and holding the windin s in place against the action ofcentrifugal orce. The grooves were not formed to effect cooling 5 of therotor and in fact their cooling function has never been recognized,since the fan is applied to such a rotor without any attention to thedirection of inclination of the grooves. That grooves in the rotor havebeen considered a detriment is clear from the fact that rotorsheretofore constructed of the bar type, whether of the inserted bar orcast bar, have been made with smooth peripheral surfaces.

I claim as my invention:

1. A rotor for a motor having very close clearance between stator androtor comprising a core having bars and end rings cast in one piecethereon, and means on the exterior surface of said rotor in the form ofgrooves extending from end to end and at a slight axial inclination forimpelling movement of air from one side of said rotor to the other whensaid rotor is in motion.

2. A rotor comprising a core and bars and end rings cast in one pieceupon said core, said core projecting slightly above said end rings, andspiral grooves in said core extending from end to end and cut to thedepth of the peripheries of said rings.

3. A rotor comprising a core and bars and end rings cast in one pieceupon said core said core projecting slightly above said end rings, andspiral grooves in said core extending from end to end and out to thedepth of the exterior surface of said rings, said grooves being directlyabove said bars.

Signed by me at Cleveland, in the county of Cuyahoga, and State of Ohiothis 23d day of March, 1929.

CHARLES B. COATES.

